The two Portal games are perhaps two of the most delightful games ever made. They were full of smart gameplay, and a story mode that was honestly funny and intelligent. And then there was GLaDOS - as far as robot personalities in videogames go, she is right up there with Claptrap for me.
Also dealing in games that can be very delightful: Zen Studios. Their Zen Pinball franchise is a many-tentacled empire with feelers in just about every franchise out there. Now they've added one more, and that is Portal. Portal Pinball will feature Chell, Wheatley, Atlas, and P-Body are all back. Get your Companion Cube to watch the trailer with you.